The present invention relates to a semiconductor device manufacturing method, more specifically, a semiconductor device manufacturing method using oblique incidence illumination.
Semiconductor devices have been continuously required to be micronized, and recently, patterns of a line width shorter than a wavelength of the exposure light source used in the manufacturing process of a semiconductor device are required to be formed.
Accompanying this, recently various illumination techniques for improving the resolution for transferring patterns are proposed. As such illumination technique, oblique incidence illumination (off-axis illumination), for example, is proposed. The oblique incidence illumination is largely divided in modified illumination and annular illumination. As major types of the modified illumination, e.g., two-point illumination (double polar illumination), wherein two apertures are formed in the aperture stop of the illumination system, is known, and four-point illumination (quadrupole illumination), wherein four apertures are formed in the aperture stop of the illumination system, is known. On the other hand, in the annular illumination, an annular aperture is provided in the aperture stop of the illumination system. The size of the aperture of the annular illumination is expressed by the outer sigma (σout), the inner sigma (σin) or others. FIG. 18 is a plan view of the conventional aperture stop of the annular illumination. In FIG. 18, the outer border indicates the border of the effective region of the aperture stop. As illustrated in FIG. 18, a ring-shaped aperture 122 is formed in the annular illumination stop. FIG. 19 is a graph of the relationship between the pitch of patterns and the depth of focus (DOF). In FIG. 19, the pitch of patterns is taken on the horizontal axis, and on the vertical axis, the DOF is taken. In FIG. 19, the DOF is the value with the exposure latitude is 4%.
In FIG. 19, the ● marks indicate the DOF given when the conventional annular illumination stop 116 illustrated in FIG. 18 is used in the illumination system. As indicated by the ● marks in FIG. 19, when the exposure is made with the conventional annular illumination stop, the DOF cannot be always sufficiently large in the range where the pitch of the patterns is about 300 nm or over.
FIG. 20A is a plan view of the layout of the mask pattern for forming holes. In FIG. 20A, on the left side of the drawing, patterns 118a for forming holes are formed on the reticle with high density. On the other hand, on the right side of the drawing of FIG. 20A, an isolated pattern 118b for forming a hole is formed on the reticle.
FIG. 20B is a graph of critical dimension-focus (CD-FOCUS) curves (Part 1). In FIG. 20B, the □ marks indicate the CD-FOCUS curve of the case of the left side of the drawing of FIG. 20A, i.e., the patterns 118a for forming holes are formed relatively densely. In FIG. 20B, the ◯ marks indicate the case of the right side of the drawing of FIG. 20A, i.e., the pattern 118b for forming a hole is formed isolated. Such CD-FOCUS curves show what influences changes of the DOF give on the resist size. In FIG. 20B, the shift of the focus in exposing the patterns is taken on the horizontal axis. On the vertical axis, the size of the patterns transferred on a resist is taken, and relative pattern sizes to the maximum size of the patterns which is set at 100 are plotted. The inclination of an upward parabola being relatively blunt means that the DOF is relatively wide, and the focus margin is relatively large. On the other hand, the inclination of an upward parabola being relatively acute means that the DOF is relatively narrow, and the focus margin is relatively small. The focus value at the summit of a parabola is called a best focus, and generally the resist size is largest at the best focus. Generally, in comparing the DOF, the focus range where the resist size is 90% or above of the resist size at the best focus is used as the effective DOF.
In FIG. 20B, as indicated by the ◯ marks, when the pattern 118b for forming a hole is isolated, the focus margin is considerably small.
As a technique of making the focus margin larger, it is proposed to use the exposure technique using together the annular illumination stop and the sub-resolution assist feature (SRAF) technique.
FIG. 21A is a plan view of the mask pattern having assist patterns for increasing the DOF. FIG. 21B a graph of CD-FOCUS curves (Part 2). As illustrated in FIG. 21A, the patterns 121 for increasing the DOF are formed around a pattern for forming a hole.
The □ marks in FIG. 21B are the same as the □ marks in FIG. 20B, i.e., the left side of the drawing of FIG. 20A, i.e., the case that the patterns 118a for forming holes are formed with relative high density. In FIG. 21B, the ◯ marks are the same as the ◯ marks in FIG. 20B, i.e., the right side of the drawing of FIG. 20A, i.e., the case that the pattern 118b for forming a hole is formed isolated. In FIG. 21B, the Δ marks indicate the case of FIG. 21A, i.e., the case that the assist patterns 121 are formed around the pattern 118c for forming a hole.
As seen in FIG. 21B, the assist patterns 121 are suitably provided (see FIG. 21A), whereby the focus margin can be increased in comparison with the case that the pattern for forming a hole is isolated (see FIG. 20A).
In FIG. 19, the ◯ marks indicate the graph of the case that the assist patterns are suitably formed on the reticle over the region where the patterns are dense to the region where the patterns are rare. As indicated by the ◯ marks in FIG. 19, the use of the SRAF technique could somewhat increase the DOF.
Following references disclose the background art of the present invention.    [Patent Reference 1]    Specification of Japanese Patent Application Unexamined Publication No. 2002-122976    [Patent Reference 2]    Specification of Japanese Patent Application Unexamined Publication No. 2003-234285
However, as indicated by the ◯ marks in FIG. 19, even the combined use of the oblique incidence illumination technique and the SRAF technique cannot always give sufficiently large DOF in the range of, e.g., about 300 nm-600 nm pattern pitch. Then, a technique which can transfer with a high resolution all patterns which are formed on a reticle at various pitches is expected.